Boom safety control system for cranes



Nov. 15, 1966 w. A. WHITMIRE 3,285,430

BOOM SAFETY CONTROL SYSTEM FOR CRANES Filed Sept. 17, 1965 5 Sheets-Sheet l 46 38 Q g i-, T-- f\ DES|RED LnvuTs ii-ii 0F BOOM SWING l if se' e4 5o L 52 k6o l H .r\\\\ in \|J u afg'L: //#'\4| /26 NVENTOR. F. 4 WILUAM A. WHITM|RE ATTORNEYS NOV. 15, 1966 W, A WH|TM|RE 3,285,430

BOOM SAFETY CONTROL SYSTEM FOR CRANES Filed Sept. 17, 1965 5 Sheets-Sheet 2 PR SSURE CLUTCH CLUTCH CLUTCH NG CAB BODY INVENTOR WILLIAM A. WHITMIRE Nov. 15, 1966 w. A. WHITMIRE 3,285,430

BOOM SAFETY CONTROL SYSTEM FOR CRANES Filed Sept. 17, 1965 5 Sheets-Sheet 5 /ZOO ' A F/C. 6

EXHAUST 2|4 BOOM UP CLUTCH BOOM CLUTCH DOWN 86 BY F/G' 7 @MI F/wn ATTORNFYS United States Patent 'F 3,285,430 BOOM SAFETY CONTRGL SYSTEM FOR CRANES William A. Whitmire, Castro Valley, Calif., assignor to Bigge Drayage Co., San Leandro, Calif. Filed Sept. 17, 1965, Ser. No. 488,178 12 Claims. (Cl. 212-39) This invention relates to heavy construction cranes and the like, and more particularly it relates to systems for automatically controlling the movement of a crane boom within predetermined limits during its operation.

Construction cranes often must be operated at locations within close proximity to obstructions such as buildings and electrical wires. Under such circumstances absolute control of the crane boom movement is essential in order to avoid serious accidents which could involve both injuries and property damage. Experience in the field long ago established the fact that operators skill cannot be relied upon to control the boom movements within safe limits under all conditions.

Accordingly, a principal object of the present invention is to provide a safety control system for automatically preventing the movement of a crane boom beyond predetermined limits during normal operation of the crane.

Another object of the present invention is to provide a system for controlling the swing of the crane boom which is adaptable to a variety of existing cranes having various types of driving and brake systems.

Another object of the invention is to provide a system for controlling the swing of a crane boom within predetermined limits which can be easily preset to the desired swing limits without the need for special tools and highly skilled labor.

A more specific object of the invention is to provide an automatic control system for controlling the movement of a crane boom within predetermined safe limits which utilizes both the normal braking force and also a braking force created by actuating the drive mechanism for swinging the boom in the opposite direction. With my invention, the boom can thus be stopped abruptly from swinging beyond a predetermined point despite high inertia factors and it can be easily released to move automatically away from the swing limit point.

Still another object of the present invention is to provide an automatic control system for cranebooms that will restrict the up and down movements of the boom within angular limits in addition to controlling the boom within predetermined azimuth limits. A further aspect ot this object is to provide an up-and-down automatic boom control system that can utilize the existing boom up-and-down drive and brake components, that is easily adjustable to control the angular limit of boom travel; that is easy to install and service; and that is durable andl yet inexpensive.

Other objects, advantages, and Afeatures of the present invention will become apparent from the following detailed description and from the drawings, in which:

FIG l is a somewhat schematic view in elevation showing a crane having a safety control system embodying the principles of the invention;

FIG. 2 is a slightly enlarged fragmentary plan view taken at the line 2-2 in FIG. 1;

FIG. 3 is an enlarged fragmentary view taken along the line 3-3 in FIG. l;

FIG. 4 is a view in section taken along the line 4--4 of FIG. 3;

FIG. 5 is a diagrammatic view of the swing control portion of my automatic boom control system according to my invention;

FIG. 6 is a partially schematic view in elevation showing the up-and-down boom control portion of my system before the boom has reached its upper limit;

3,285,430 Patented Nov. 15, 1966 ICC FIG. 7 shows the boom of FIG. 6 after it has reached its upper limit.

FIG. 8 is an enlarged view in section taken along the line 8-8 of FIG. 7.

Referring to the drawings, FIG. l shows somewhat schematically a typical crane 20 comprising general-1y an operators cab 22 and a boom 24 mounted pivotally thereon for up and down movement'. Like all conventional cranes, the cab is adapted to swing or rotate in a horizontal plane on a crane chassis 26 which is provided with suitable wheels :or crawler tracks 28 to give it mobility. The exact details of how the control cab is mechanically mounted on the crane chassis are not shown since they are not essential to the invention. Generally, on such cranes the cab has a cylindrical lower body portion 30 which is rotatably supported on a central shaft within an azimuth ring 32 fixed to the chassis. The power for driving the cab rotationally in either direction on the chassis may be provided by a separate self-sustaining engine or some other suitable power source (not shown), such as electrical or hydraulic drive motors. Itis conventional in most cranes to drive the cab in rotation through a gear system controlled by a main clutch or -by separate clutch devices that connect the gear systems to the power source. Such clutch devices, which may be either mechanical or electrical, are adapted to engage the power drive system and thereby swing the cab and its boom in either direction. Manual control of the clutches is normally provided by a system of electrical relays and/ or by manual hydraulic or pneumatic control valves or switches controllable by the crane operator. To Ihelp in stopping the swinging cab and its boom a braking device is also provided on the crane 20 and again is shown only schematically be.

cause its mechanical details are not essential to the present invention. On conventional cranes such a brake may comprise generally one or more friction devices which are movable by actuation means to engage the cylindrical body portion 30 on the cab body. Normally, the power to the actuation means is controlled manually by the crane operator by means of a hand or foot lever. rThe automatic control of such actuation means is also a part of my invention and will be described later on with reference to FIG. 5.

`The crane 20 is also provided with -a suitable means for raising or lowering the boom, and automatic control of this mechanism is also part of my boom safety control system. `Again, the details of the actual boom-raising mechanism are not critical to the present invention and such isshown typically in FIG. l as comprising a conventional power driven winding drum 34 to which is attached a cable 36 connected to the boom.

Theforegoing general description is provided to emphasize the fact that the present invention provides a safety control system for automatically controlling the movement of a crane boom Within predetermined set limits. It is not limited in its application to only tone type of crane having a particular driving and braking system for its boom, but is instead an automatic system which can be superimposed on a wide variety of manual control systems in various existing cranes.

Proceeding now with a more detailed description of my automatic control system, FIG. 2 shows a plan view in section of the azimuth ring 32 with azimuth limits dened within which its boom might normally be restricted in order to prevent any contact with wires, trees, or other obstructions. According to my invention, once the desired limits of boom swing are determined, they can be set by adjusting the fixed position of a pair of left and right cam-like actuating members 38 and 40 on the azimuth ring 32. The latter, as shown in .greater detail in FIGS. 3 and 4, each comprise a relatively short, channelshaped lower body portion 41 having an elongated cover member 42 of uniform width which extends the length of the lower body portion and forms a cam track thereon with uphill and downhill ramp portions 44 and 46 at its opposite ends. Both actuating members fit loosely over the azimuth ring 32 and each is Slidable to any preselected location thereon. A pair of set screws 48 in the lower channel portion are used to secure each actuator irmly in place when moved to the desired position.

Attached to the cylindrical body portion 30 or the underside of the crane cab 22 near the azimuth ring 32 is a switch box 50 which cooperates with the actuator members 38 and 40 to control the swing of the cab and its boom in opposite directions. Mounted within the switch box 50 are four microswitches 52, 54, 56 Aand 58, arranged in left and right pairs, each one having a switch arm that extends downwardly and outwardly from the box. To the ends of the arms of the aforesaid switches are attached cam followers or rollers 60, 62, 64 and 66, respectively. These rollers are spaced apart and are substantially aligned with each other in the same vertical plane and with the actuator members 38 and 40 as the cab rotates. The left microswitches 52 and 54 serve to actuate the automatic lcontrol system when the crane boom moves to its left limit position and similarly the right microswitches 56 .and 58 operate when the right limit position is reached. For example, as the crane cab rotates to the left, the rst left cam follower 60 will engage the actuator member 38 and actuate the first microswitch 52. The cab must then continue to move a signiiicant amount in the same direction before the second microswitch 54 will also be actuated due to the second cam follower 62 engaging the actuator 38. The distance between the first and second cam followers 60 and 62 for the switches 52 and 54 determines the degree of rotation of the cab that must take place before the second switch 54 is actuated.

What happens in my automatic boom swing control system when the cam followers actuate their respective switches as the boom swings out of its predetermined safety zone may be explained by first describing the schematic diagram of my -control system shown in FIG. 5.

The outermost or rst cam followers 60 and 66 which are rst to engage either of the actuator members 38 or 40 as the crane cab rotates, are each connected from their own switches 52 and 58 to a single-pole, double-throw on-off switch 68 for the system. Electrical power is supplied through the switch 68 when the crane is operating normally and thence through a lead 70 and through the rst microswitches 52 and 58 which are connected in series in the switch box 50, and then through a lead 72 to a green light 74 located in the operators cab. Assuming, for example, that the crane swings to its left limit position and the rst microswitch 52 in the switch box 50 has been actuated by its cam follower 60. This stops the flow of current to the .green light 74 and directs it instead through another lead 76, connected between opposite poles'of the switches 52 and 58, and thence through a lead 78 to an amber warning light 80 located near the operator in the cab. The latter lead 78 is also connected by a branching lead 82 to a buzzer 84 which will give the oper-ator an audible warning that the crane has moved to its azimuth limit.

The second or innermost cam followers 62 and 64 control the switches 54 and 56 which are referred to as the left and right swing control switches, respectively. If

v the crane boom continues to swing in the same direction after the first warning switch 52 or 58 has been actuated by its cam'follower to energize the amber light and the buzzer as described above, the second cam follower 62 or 64 engages the adjacent cam actuator and trips its respec# tive swing switch. In accordance with the invention, ac-

, Y tuation ofV either one of the swing switches 54 and 56 conj trols both the drive system and the brake systern of the g crane, thereby immediately stopping movement of its cab and boom. Vshown in the schematic diag-ram of FIG. 5, both the left and right swing switches 54 and 56 are connected in parallel by a pair of leads 86 and 88 connected to the power lead 70. The left swing switch 54 is also connected by a lead 90 to a first brake isolation relay 92, and similarly the right swing switch 56 is connected by a lead 94 to a second brake isolation relay 96. These brake isolation relays provide a means for combining the automatic brake actuation control with automatic cont-rol of the drive system and with a minimum of circuitry. In effect, the brake control system is isolated from the clutch or drive control portion of the system so that it will operate if either left or right swing control switches are activated.

The brake isolation relays are also connected in parallel by means of a pair of branching leads 98 and 100 to a lead 102 extending from the main electrical power lead 7 0.

The branching leads 98 land 100 terminate within the brake isolation relays at normally open contact points 104 and 106, respectively, which may be closed by a pair of switch arms 108 and 110, respectively, within the relays 92 and 96. The relay switch arms are controllabile by means of current through the leads 94 and 90 from the left and right swing switches, and they are also connected together in parallel by a lead 112. This latter lead is also connected in series to an ioverride switch 116 and thence by another lead 114 to the solenoid on an electrically operated air valve 118. The llatter, which may be a simple, single-acting slide type valve, is connected by an inlet conduit 120 to a source 122 of fluid under pressure and by an outlet conduit 124 to la brake actuation device 126. The latter, as shown schematically and not in detail, may comprise an actuating cylinder connected by means of a suitable linkage to act positively on the swing brake 130. While the aforesaid arrangement is representative of typical crane braking systems, the valve 118 could be connected to actuate various other brake systems such as one wherein air is released or bled from a can or cylinder to release a spring that will supply the braking force.

The power lead 90 from the left swing switch 54 is connected by an extended lead 132 to an actuating solenoid 134 of a valve 136, such as an air valve, which controls the left drive clutch 138. Similarly, the power lead 94 from the right swing switch 56 is connected by an extended lead to an actuating solenoid 142 of another valve 144 that controls the right drive clutch 146. The first and second brake isolation relays 92 and 96 are therefore connected in parallel with the controlling solenoids 134 and 142 of the left and right Aswing valves 136 and 144, respectively.

While the actuating systems may differ on various crane systems and while the principles of my invention are applicable to different systems, the embodiment shown assumes the swing control valves 136 and 144 are conventional air valves of the dual acting type, each being supplied with lair, under pressure, from a compressed air source at two inlets, each Valve also having two outlet ports. The left swing valve has one outlet connected by a conduit 148 directly to the left clutch actuator 138. Similarly, .an outlet of the right swing valve 144 is sconnected by a conduit 150 directly to the right clutch actuator 146. A branch exhaust conduit 152 interconnects the conduit 148 from the left swing valve and a second outlet of the right swing valve, and similarly a conduit 154 interconnects the conduit 150 from the right swing valve and the second outlet lof the left swing valve. A manual control valve 156 for controlling the swing valves 136 and 144 during normal operation is provided in the operators cab. Through a main conduit, the valve 156 receives power such as compressed air and directs it through a pair of outlet conduits 160 and 162 `to the rst inlets of the left and right valves 136 and 144, respectively. Connected in parallel with the manual control valve 156 are a pair of supply conduits 164 and 166 which connect with the second inlets on the left and right swing valves, respectively.

The automatic operation of these swing valves in conjunction with the brake actuation in accordance with my invention will be discussed later.

An integral p-art of my system for automatically controlling the swing of the crane cab and its boom within azimuth limits is a means for automatically controlling the up and down movement of the boom. The drum 34 shown in FIG. l is a conventional means on cranes for moving the boom up and down, and it is generally driven by a power source (not shown) through a clutch that may be actuated by any suitable means, c g., either pneumatically or hydraulically. A braking means for the up-anddown boom drive system, which may be applied to the drum, Imay also be actuated by hydraulic, pneumatic, or even electric power. As with the previously described swing control phase of any system, the automatic system for controlling up and down boom movement is also readily adaptable to existing boom raising and lowering systems on cranes that heretofore were manually controlled. As illustrated schematically in FIGS. 6 and 7, this portion of my boom safety control system comprises an adjustable arm 168 that is pivotally connected to a structural portion 170 of the crane cab 22 at a location in close proximity tothe lower end of the boom 24. The arm 168 is connected at one end by means of a pin 172 in cooperation with a means for holding it in a preset position such as a friction hinge 174. The latter, as shown in FIG. 8, may comprise a first plate or bracket 176 fixed to the cab structure 170 and supporting the pin 172 and a parallel plate t-o which is attached the arm 168. Between these plates in a Idisc 180 made of friction lining material. A take-up nut 181 on the threaded end of the pin 172 is used with a spring 182 to press the plates together when tightened, thereby holding the arm 168 at any preselected angular position above the boom. Fixed to the end of the arm is a microswitch 184 having a switch arm 186 that extends outwardly and slightly downwardly so that a follower 188 on its outer end will contact the boom well before the boom can Contact the arm itself. The inner end yof the switch arm comprises one of a pair of contact points 4and is connected to a Iground 190 within the switch 184. The other contact point 192 is connected to a lead 194 extending from the arm 168 and to the power supply lead 'i0 of the -crane electrical system. Connected in parallel between the power lead and the switch 184 is a red light 196 located near the operators station and the actuating solenoid 198 of a double-acting valve 200. This latter valve is supplied by compressed air (or hydraulic pressure) from a source 201 through a conduit 202 and a manual control valve 203 to an inlet port 204. A longitudinally movable cylinder 206 within the valve controls the flow of fluid through either of two `outlet ports 208 and 210. The tirst outlet port 208 provides an exhaust from the valve 200 and the second outlet port 210 is connected to conduit 212. In a typical boom drive system the latter may be connected in parallel to a boom-up clutch control device 214 which engages to drive the boom wind-up drum 34 Iand also to a shuttle valve 215 that is connected to a drum brake actuator 216. A boom-down clutch control device 217 may also be connected to a conduit 218 that extends from the power source 201 through another manual valve 219 to the other end of the shuttle valve 215. The clutch 217 controls the downward boom movement, and it could also be -automatically controlled by an arm similar to the arm 168 and positioned to l0- oate a limit switch that would be actuated by the downward boom movement. While the duplicate system for automatically controlling the downward boom movement has not been shown, it will become apparent from the description of the 11p-boom control system.

The proper position for the arm 168 is best determined by first moving the boom 24 upwardly slowly to its maximum allowable position and then adjusting the arm so that the follower 188 on the switch-arm 186 is just engaged with the boom 24. The arm 168 is then locked in position by the friction hinge 174 near its pivotal connection. When the boom is operating within normal limits the microswitch 184 is open, as shown in FIG. 6, and air or fluid flows through the Valve 20'0 and out through the conduit 212 to the boom-up clutch 214 causing it to engage and drive the drum 34. Simultaneously, air from the Valve 200 may also be supplied through the shuttle valve 215 to the brake actuator 216, as shown, causing it to stay in the off position. Now, if the boom moves upward out of its safe operating zone, it engages the follower 188 and the switch arm 186 thereby closes with the contact point 192 of the switch (FIG. 7). This causes current to flow to -both the red light 196 and to the solenoid 198 of the., Valve 200. Energization of the solenoid causes the pilot air pressure to move the valve cylinder 206, and the compressed air now is diverted by the valve to the exhaust or return conduit 208. This causes air to bleed from the boom-up clutch 214 and the brake actuator 216 and thus the boom-up driving force ceases as the brake 220 is automatically applied to the drum 34. The illustrations in the drawings of my boom control system are, of course, schematic, and it is to be understood that various combinations of mechanical controls, clutches, brakes and equivalents thereof can be used to provide the desired operation of the system within the scope of the invention. Also, as stated previously, a similar system could be used for automatically controlling the boom-down movement.

To review the operation of the entire automatic control system, it may be assumed that the left and right actuators 38 and 40, as well as the arm 168, have been locked in preselected positions in accordance with the desired limits of swing for the boom. During normal operation of the crane between these two limiting actuators, current flows from an electrical power source through the leftand right-hand caution switches 52 and 58 to the green light 74 at the crane operators station within the cab. When the boom swings into a dangerous position, for example, to the extreme left, the actuating member 38 will be engaged by the first left swing cam follower 60 extending from the switch box 50 on the crane. As this roller or follower is raised by the ramp portion 44 of the actuator 38, the left caution microswitch 52 is tripped and causes current to stop owing to the green light 74 and to flow instead to the amber warning light and the buzzer 84. If the amber light and the buzzer fail to warn the operator, and the cab and boom continue to -swing in the same direction, the second left swing cam follower 62 on the switch box 50 engages and rolls up the ramp end of the cam actuator 38 until it trips the left swing switch 54. Closing the left swing switch causes current to ow through the lead and actuates the pneumatic valve 136. Current also ows through the lead 90 to the first brake isolation relay 92 causing it to trip and to complete a circuit from the main electrical power source, through the override switch 116 to the valve 118 that controls the brake actuator 126. Simultaneously, current through the relay 92 and the lead 112 flows through a lead 119 to a red light 121 located in the operators cab. The actuation of the brake valve 118 causes the actuator 126 to immediately apply a braking force tending to stop the rotational movement of the cab. The simple lever and friction brake member shown are merely symbolic of any suitable braking which could be utilized within the scope of the invention.

Actuation of the brake, as described, occurs simultaneously with the automatic control of the swing drive system to overcome the inertia of the cab and its boom, to bring them to an immediate stop. This quick stopping ability is accomplished in my automatic system by not only cutting off the driving power in the initial direction of movement but by automatically actuating the driving power in the opposite direction, the latter thereby serving as an additional braking means. For example, in the situation described thus far, when the left swing switch 54 is closed by the movement of the cam follower 62, current supplied to the brake isolation relay 92 also flows to the left swing valve or control unit 136. Just prior to the actuation of the left swing switch 54, the left swing valve 136 was operating to supply power to the left clutch 138 to drive the cab and its boom to the left. Now, when current to the valve 136 causes it to actuate, the power to the left clutch is cut off and it is disengaged. Simultaneously, the power (e.g., compressed air) entering the valve 136 is diverted through the conduit 154 to the right clutch 146, thereby causing it to engage. Thus, if the cab swings into a danger zone it is not only stopped immediately,

'but the driving force on the cab is automatically reversed so that an additional force is applied to the cab to help brake it and possibly move it in the opposite direction out of the danger zone. The reversing drive force may not be sutiicient to overcome the force of the brake itself that has automatically been applied, so it may be necessary for the operator to manually actuate the override switch 116 after the cab and boom have been stopped and the red light 121 has gone on. This will break the circuit to the brake valve 118 causing it to return to its off position and to release the brake actuator 126 thereby enabling the opposite driving clutch to turn the cab back away from the danger zone. As the cab swings back, the

cam followers 60 and 62 roll off of the cam actuator 38 and the automatic control system remains deactivated until the cab again swings to an extreme azimuth position.

From the foregoing it should be apparent that the present invention provides an integrated automatic control system for a crane that will automatically control both the up and down boom movements in the vertical plane and the degree of left and right swing in the horizontal plane. The present system is readily adaptable to a variety of conventional cranes having different driving and braking arrangements, and it can utilize existing drive and brake components as well as the common power supplies of electricity and compressed air (or hydraulic pressure) that are already available in such cranes. The unique arrangement of interconnected control components provides for fast, sure stops even if the crane boom is caused to swing at a high rate into a danger zone. When installed, my safety system enables the crane to be operated with greater speed and eiciency as well as safety because the operator is relieved of the requirement to maneuver the boom manually within narrow limits.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

I claim:

1. In combination with a crane, including a cab rotatably mounted on a chassis and a boom pivotally attached to said cab, manually controllable left and right drive means for swinging said cab in both directions in a horizontal plane and swing brake means for opposing the swing of said cab, drive means and brake means for controlling the boom up and down movement, a safety control system for automatically controlling the movement of the boom within predetermined angular limits in the horizontal plane, said system comprising:

azimuth control means secured to said chassis at preselected spaced apart locations beneath said cab;

.an electrical circuit including a iirst switch means on said cab actuated by a said azimuth control means when said cab swings beyond a predetermined safe limit position with respect to the crane chassis;

means for actuating said swing brake means to stop said cab in response to actuation of said switch means;

means also responsive to` actuation of said switch means for simultaneously -disengaging the drive means tending to swing the cab and its boom outside its safe operating area.

2. In combination with a crane, including a cab rotatably mounted on a chassis and a boom pivotally connected at one end to said cab; manually controllable left and right drive means for swinging said cab in both directions in a horizontal plane and swing brake means for opposing the swing of said cab, drive means and brake means for controlling the boom up and down movement,

' a safety control system for automatically controlling the swing of said cab within predetermined angular limits defining a safe operating area, said system comprising:

a pair of actuator means secured to said chassis at preselected spaced apart locations beneath said cab;

an electrical circuit including switch means on said cab actuated by a said actuator means when said cab swings beyond a predetermined safe limit position with respect to the chassis; means for actuating said swing brake means to stop said cab in response to actuation of said switch means;

means also responsive to actuation of said switch means for simultaneously disengaging the drive means tending to swing the cab and its boom outside its safe operating area. 3. In combination with a crane, including a cab rotatably mounted on a cassis .and a boom extending from said cab, manually controllable left and right drive means for swinging said cab in both directions in a horizontal plane and brake means for opposing the swing of said cab, a safety control system for automatically stopping the swing of said cab and its boom at predetermined angular limits defining a safe operating area, said system comprising:

a pair of actuator means secured to said chassis at preselected spaced apart locations beneath said cab;

switch means on said cab actuated by a said actuator means when said cab swings beyond a predetermined safe limit position with respect to the chassis;

means for actuating said brake means to stop said cab in response to actuation of said switch means;

and means also responsive to actuation of said switch means for simultaneously disengaging the drive means tending to swing the cab and its boom outside its safe operating area.

`4. In combination with a crane, includ-ing a cab rotatably moamted on a chassis and a boo-m extending from said cab, manually controllable lleft and right drive means for swinging said carb in both directions in a horizontal plane and brake means for opposing the swing of said cab, a safety control system for automatically stopping the swing of said cab and its boom at predetermined angular limits defining .a safe operating area, said system compris- 111g:

a pair of actuator means secured to said chassis at preselected spaced apart locations beneath said cab; switch means on said caib actuated by a said actuator means when said cab swings bey-ond a predetermined `safe limit position with respect to the chassis; means for actuating said brake means to ystop said cab in response to actuation of said switch means;

and means also responsive to actuation of said switch means yfor simultaneously disengaging the drive means tending, to swing the cab and its boom. outside its safe oper-ating area and for engaging the other drive means tending to swing the cab in the opposite direction.

5. In combination with a crane, including a cab rotatably mounted 4on a chassis having an azimuth ring spaced radially from the axis of rotation lof said cab and a boom extending 'from said cab, manually controllable left and right drive means for swinging said cab in both directions in a horizontal plane and bra-ke means for opposing the swing of said cab, a safety control system 'for automatically stopping the swing of said cab and its boom at predetermined angular limits defining a safe operating area, said system compri-sing:

a pair of adjustable actuator means secured to the azimuth ring of said chassis at preselected spaced apart lo cations beneath said cab;

a switch box fixed to said cab and housing a series switch means each having a movable arm with a follower at the end thereof, said lfollowers being aligned with and adapted to engage said actuator means when said cab swings beyond a predetermined sate limit .position with Irespect to the chassis;

means for actuating said brake means to stop said cab in response to actuation Iof one of said switch means;

and means also responsive to actuation of said same switch means for simultaneously disengaginlg the drive means tending to swing the cab and its boom outside its safe operating area.

6. The system as described in claim wherein each said actuator means has a lower portion that lits slidably ove-r said azimuth ring, a track-like cover fixed to said lower portion :having .an -up-sloped ramp portion at one end, and means for lirmly securing said actuator means to said azimuth ring at any preselected position.

7. In combination with a crane, including a cab rotatably mounted on a chassis and a boom extending from said cab, manually controllable left and right drive means for swinging said -cab in both directions in -a horizontal plane and brake means for opposing the swing of said cab, a safety control system for automatically stopping the swing of said `cab and its boom 4at predetermined angular limits defining a safe operating area, said system comprising:

switch means fixed to said cab;

means secured to said chassis at preselected spaced apart locations beneath said cab ffor actuating said switch means when said -cab swings beyond a predetermined safe limit position with respect to the chassis;

valve means Afor `eontrolhng said brake means;

.means tor actuating said valve means to operate said rbrak/e means and thereby stop said cab in response.

to actuation of said switch means;

and means including a pair of valves also responsive to actuation of said switch means lfor simultaneously disengaging one drive .means tending to swing the cab and its boom outside its safe operating area, and [for engaging the yother drive means for providing a cab swinging force in the opposite direction. 8. In combination with a crane, including a cab rotatably mounted on a chassis and a boom extending irom said cab, manually controllable left and right drive means for swinging said cab in both directions in a horizontal plane and brake means for opposing the swing of said cab, a safety ycontrol system ttor -automatically stopping the swing of said cab .and its boom at predetermined angular limits defining a safe operating area, said system comprising:

a pair of actuator means secured to said chassis at preselected spaced -apart `locations beneath said cab;

switch mean-s on said cab actuated by a said actuator means when said cab swings beyond a predetermined safe limit position with respect to the chassis;

means responsive to actuation of said switch means for simultaneously disengaging Ithe drive means tending to swing the cab and its boom outside its safe operating area and for engaging the other drive means tending to swing the cab in the opposite direction;

4and means including a pair of isola-tion relays for ac tnatin-g said lbra-ke means to help stop said cab when either of said drive means are also actuated in response to actuation of said switch means.

9. In combination with a crane, including a cab rotatably mounted on a chassis having an azimuth ring spaced radially Ifrom the axis of rotation of said cab and a boom extending from said cab, manually controllable left and riglht drive means for swinging said cab fin both directions in a horizontal .plane and brake means for opposing the swing of said cab, a safety control system for automatically stopping the swing of said cab and its boom at predetermined angular limits defining a safe operating area, said system comprising:

a pair of adjustable actuator means secured to the azimuth ring of said chassis at preselected spaced apart locations beneath said cab;

a switch box fixed to said cab;

a iirst pair olf switch means within said box each having a movable arm with `a follower at the end thereof, said followers being aligned with Iand `adapted to engage either of said actuator means when said cab swings in either direction beyond a predetermined safe limit position with respect to the chassis;

a pair of electrical circuits each controlled by one said switch means and each connected to an isolation relay and an electrically lcontrollable valve means in parallel, a said latter valve means being connected with and adapted to Icontrol actuation of said left and right drive means;

brake control means electrically connected -to both said isolation relays;

whereby the contact of a follower with a said actuator means as the cab swings beyond a predetermined limvit causes the closing of a said switch means resulting in actuation of said brake means through its isolation relay Iand simultaneous actuation of a valve control means causing the enga-ged drive means to disengage.

10. The apparatus as described in claim 9 including means interconnecting said controllable valve means for said drive means for causing the other drive means to en- 'gage and thereby tend to `move the cab in the direction opposite to its movement prior to actuation of the switch.

11. The apparatus as described fin claim 9 includ-ing a manually operable override switch between said isolation relays and said brake control means.

12. The apparatus as described in olaim 9 including a second pair of switch means with said .box each having a movable 'arm with a tto'llower at the end thereof, said yfollowers being spaced outwardly from the followers of said iirst switch means and also aligned with and adapted to engage either of said actuator means when said cab swings in either direction beyond a predetermined safe limit position; and an electrical circuit controlled by said second switch means containing a warning means located near the 4crane operators station on said chassis.

References Cited by the Examiner UNITED STATES PATENTS 1,775,435 9/1930 Lichtenberg 212-39 2,376,019 5/1945 Thomas 212-39 `2,502,420 4/1950 Carrell 212-66 2,529,193 11/-1950 nuera 212-39 FOREIGN PATENTS 1,171,131 5/1964 Gemany.

989,679 4/1965 oreatraain.

ANDRES H. NI'ELSEN, Primary Examiner. 

1. IN COMBINATION WITH A CRANE, INCLUDING A CAB ROTATABLY MOUNTED ON A CHASSIS AND A BOOM PIVOTALLY ATTACHED TO SAID CAB, MANUALLY CONTROLLABLE LEFT AND RIGHT DRIVE MEANS FOR SWINGING SAID CAB IN BOTH DIRECTIONS IN A HORIZONTAL PLANE AND SWING BRAKE MEANS FOR OPPOSING THE SWING OF SAID CAB, DRIVE MEANS AND BRAKE MEANS FOR CONTROLLING THE BOOM UP AND DOWN MOVEMENT, A SAFETY CONTROL SYSTEM FOR AUTOMATICALLY CONTROLLING THE MOVEMENT OF THE BOOM WITHIN PREDETERMINED ANGULAR LIMITS IN THE HORIZONTAL PLANE, SAID SYSTEM COMPRISING: AZIMUTH CONTROL MEANS SECURED TO SAID CHASSIS AT PRESELECTED SPACED APART LOCATIONS BENEATH SAID CAB; AN ELECTRICAL CIRCUIT INCLUDING A FIRST SWITCH MEANS ON SAID CAB ACTUATED BY A SAID AZIMUTH CONTROL MEANS WHEN SAID CAB SWINGS BEYOND A PREDETERMINED SAFE LIMIT POSITION WITH RESPECT TO THE CRANE CHASSIS; MEANS FOR ACTUATING SAID SWING BRAKE MEANS TO STOP SAID CAB IN RESPONSE TO ACTUATION OF SAID SWITCH MEANS; MEANS ALSO RESPONSIVE TO ACTUATION OF SAID SWITCH MEANS FOR SIMULTANEOUSLY DISENGAGING THE DRIVE MEANS TENDING TO SWING THE CAB AND ITS BOOM OUTSIDE ITS SAFE OPERATING AREA. 